After living for several years in Germany, it is possible to apply for German citizenship (naturalisation). The following pre-requisites for naturalisation must be fulfilled:

• 8 years of residency in Germany (a shorter time is possible if particular efforts have been made toward integration or under exceptional circumstances)
•  a secure source of income to cover the cost of living
• no criminal record
• sufficient German skills (B1)
• a successful citizenship test

The necessary application forms are available from your naturalisation authority (Einbürgerungsbehörde). You can find out what agency that is from the immigration authority (Ausländerbehörde) where you live.